1. Technical Field
The present invention relates to constant velocity universal joints used in power transmission devices of, e.g., automobiles and various kinds of industrial equipment, and more particularly to sliding type constant velocity universal joints.
2. Description of the Related Art
There is known a drive-power transmission structure for automobiles, using a pair of sliding type constant velocity universal joints, where each universal joint in the pair is disposed between an axle of the left or the right wheel and a differential gear system via an intermediate shaft (Patent Literature 1). In the sliding type constant velocity universal joint described above, the intermediate shaft is subject to axial displacement and therefore indefinite in position, potentially leading to a situation that the other end of the intermediate shaft will make contact with an inner end surface of an outer joint member of the other constant velocity universal joint in the pair, resulting in generation of noise and/or vibration.
In order to prevent generation of these noise and vibration, there is utilized an arrangement where, in one of the constant velocity universal joints, a coil spring is placed in a compressed state, between the inner end surface of the outer joint member and the said other end of the intermediate shaft, thereby urging the intermediate shaft toward the other constant velocity universal joint in the pair and thereby pressing the other end of the intermediate shaft to a receptacle member which is provided in the inner end surface of the outer joint member.
FIG. 6 shows such a conventional tripod sliding type constant velocity universal joint which includes the coil spring as described. The figure shows a state where an operating angle is zero degree. This constant velocity universal joint is implemented by an assembly of an outer joint member 11, an inner joint member 12, an intermediate shaft 13, a coil spring 14 and a spring receptacle member 115. The intermediate shaft 13 is generally provided by a torque transmission shaft; however, the intermediate shaft 13 so termed herein refers to a torque transmission shaft which is interjacent to the other sliding type constant velocity universal joint.
The outer joint member 11 is constituted by a cup-shaped mouth portion 16 which has one open end, and a stem portion 17 protruding coaxially therewith, out of the closed end of the cup in a direction away from the mouth portion 16. An axial guide groove 18 is formed at a one-third equally dividing position in a circumferential direction of an inner circumferential surface of the mouth portion 16. Also, a spring receptacle recess 19 is formed at a center in an inner bottom surface. The stem portion 17 is formed with a spline 21 (the term includes serrations; the same definition applies hereinafter).
The inner joint member 12 has a radially protruding journal shaft, i.e., so called trunnion shaft 24, at a one-third equally dividing position around a boss 23. The boss 23 is formed with a spline hole 22 at its center. The trunnion shaft 24 is elliptically cylindrical, and a roller assembly 28 which is constituted by an inner ring 25, an outer ring 26, and needle rollers 27 placed therebetween is pivotably fitted with a certain margin in the direction of trunnion shaft 24. Further, the roller assembly 28 is fitted rotatably in the guide groove 18.
The inner ring 25 and the needle rollers 27 are integrated with the outer ring 26 by snap rings 29a, 29b which are placed between end surfaces of the outer ring 26 and of the inner ring 25 on both of the inner and the outer sides.
The intermediate shaft 13 has an end portion formed with a spline shaft section 30. The spline shaft section 30 has its tip surface formed as a convex spheroidal surface 31. The spline shaft section 30 is fitted through the spline hole 22 of the inner joint member 12, and is fastened in place by a snap ring 32. The convex spheroidal surface 31 protrudes inward of the mouth portion 16, from the spline hole 22.
As shown in FIG. 8, the spring receptacle member 115 is a cup-shaped member having a bottom plate 33 which is formed into a concave spheroidal surface for contact with the convex spheroidal surface 31, and a low-walled cylindrical portion 134 which rises from a circumferential edge of the bottom plate 33 toward the spring receptacle recess 19. The cylindrical portion 134 rises by a height h1, which is approximately equal to two windings of the coil spring 14 shown in FIG. 6 when the operating angle is zero degree. A seat 135 for the coil spring 14 is provided by a corner regions made by an inner bottom surface of the bottom plate 33 and inner circumferential surface of the cylindrical portion 134 rising therefrom.
The coil spring 14 is placed in a compressed state between the spring receptacle recess 19 and the spring receptacle member 115. On the spring receptacle member 115 side, the coil spring 14 has its end pressed onto the seat 135, i.e., onto the circumferential edge region of the bottom plate 33 along the inner circumferential surface of the cylindrical portion 134.
FIG. 7 shows an operating state at a certain predetermined operating angle θ (the angle in the figure is 15 degrees). Under this state, there can be a situation where the spring receptacle member 115 slips and tilts in a direction away from tilt of the intermediate shaft 13. Simultaneously, an end portion of the coil spring 14 moves away, resulting in a situation that said end portion of the coil spring 14 is bent with respect to the other end portion which is supported by and fixed in the spring receptacle recess 19.
Although the conventional constant velocity universal joint described above has no problem when the operating angle θ is zero degree or the angle is small, the spring receptacle member 115 tilts to a greater extent as shown in FIG. 7 once the operating angle θ reaches a certain large angle, allowing an edge 37 on top of the cylindrical portion 134 to come off the outer ring 26, resulting in interference with an intricately-shaped portion of the roller assembly 28 including steps formed by the snap ring 29a, an end surface of the inner ring 25, etc. on the back surface of the roller assembly 28. Such an interference destabilizes rotation of the roller assembly 28, and can adversely affect operability of the constant velocity universal joint.
One attempt to solve the above-described problem is implemented in a sliding type constant velocity universal joint (Patent Literature 2), in which the cylindrical portion 234 is given an increased height h1 so that the edge 37 would not make interference with the back surface of the roller assembly 28.
In this case, as shown in FIG. 9, the cylindrical portion 234 has a height h2 (>h1), being higher by one additional wind of the coil spring 14. More precisely, as shown in FIG. 10, the cylindrical portion's height h2 is increased to an extent that the cylindrical portion 234 of the spring receptacle member 215 has its outer circumferential surface always in contact with the outer ring 26, not allowing the edge 37 to make contact therewith before the operating angle θ reaches the maximum angle and even after it has reached it. Such a setting gives a fair level of stable operation since the edge 37 does not come off the outer ring 26 even when the maximum angle is reached and therefore there is no interference with the back surface of the roller assembly 28.